Effects of Water-to-Cement Ratios on the Properties of Magnesium Potassium Phosphate Cement Prepared with Lithium-Extracted Magnesium Residue

Salt lake magnesium phosphate cement (SLMKPC) was prepared by mixing potassium dihydrogen phosphate (KH2PO4) with lithium-extracted magnesium residue (MR). The hydration-hardening process and the variation in the phase composition and microstructure of hydration products with the change of the water-cement-ratio (W/C) were studied by measuring the setting time, hydration exothermic temperature, and compressive strength of the hardened slurry. It was found that W/C ratios had significant effects on the setting time, hydration exothermal temperature curve, and compressive strength of SLMKPC. With the increase of W/C, the setting time was prolonged significantly. The exothermic hydration peak temperature first increased and then decreased, and the number of exothermic peaks gradually changed from one to two. The optimal compressive strength was obtained when W/C = 0.2–0.3. Hydration products changed significantly with the increase of W/C, the MgKPO4·6H2O (MKP) in the matrix was more stable when W/C = 0.2 and 0.3 than when W/C = 0.25, 0.35, and 0.4. When W/C = 0.3, SLMKPC had a compact structure with a certain operating space and better mechanical properties.